This change is needed in preparation for making Interpreter::getStackTrace() private in https://bugs.webkit.org/show_bug.cgi?id=119575.
Created attachment 208350 [details] The patch. This patch has already been reviewed by Oliver Hunt in https://bugs.webkit.org/show_bug.cgi?id=119575. I'm submitting it here so that I can land it separately as a sub-patch.
Landed in r153823: <http://trac.webkit.org/r153823>.